The present invention relates to a method of fabricating a semiconductor device by forming a monocrystalline or substantially monocrystalline semiconductor layer on an insulating or amorphous layer.
There is known a method for fabricating a semiconductor device by forming a monocrystalline or substantially monocrystalline semiconductor layer on an insulating or amorphous layer, in which, as shown in FIG. 1, a polycrystalline silicon layer 12 is formed on an insulating layer 10 of amorphous material such as SiO.sub.2 by a CVD method, and the polycrystalline layer 12 is irradiated with a laser beam 20 to melt the latter to thereby increase the grain size thereof and partially convert the polycrystalline structure into a monocrystalline structure.
In another conventional method by which the crystal structure can be further improved, a grating 11 is formed on the amorphous insulating layer 10 as shown in FIG. 2a; a polycrystalline silicon layer 12 is formed on the insulating layer 10 having the grating and then the silicon layer 12 is annealed with a laser beam to form a monocrystalline silicon layer 13 as shown in FIG. 2b. In this method, the crystal orientation is regulated due to the existence of the sidewalls of the grooves of the grating, and thus it is possible to improve the crystallization.
With these conventional methods, however, the improvementin the crystallization is limited by the fact that the grain size of the polycrystalline silicon layer formed by the CVD method is increased by the annealing using one irradiation with the laser beam, and it is difficult to convert an entire polycrystalline silicon layer whose grain size is on the order of 0.1 .mu.m into a monocrystalline silicon layer at one time. That is, in order to convert polycrystalline silicon spread over a wide area into monocrystalline silicon, it is necessary to use a laser of high power. However, the use of such a high power laser beam causes the polycrystalline silicon layer to peel off the amorphous SiO.sub.2 layer, and the process margin is insufficient.